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The Planet Mars. Image credit: NASA

The Planet Mars. Image credit: NASA

Planet Mars is the 4th planet from the Sun, and is named after the Roman god of war; perhaps for its red coloring, to signify blood on the battlefield. Because of this color, Mars is also referred to as the “Red Planet”. When seen in a telescope, Mars does appear red. This red color comes from the oxidation of iron-rich minerals on its surface. You could say that Mars is rusty. The Babylonians also named the planet after their god of war, fire, and destruction. The Greeks also called it after their god of war. Other culture such as the Chinese, Persians, and Japanese, all had references to the planet in ancient texts.

Mars orbits at an average distance of 228 million km from the Sun, or 1.52 astronomical units (1 AU is the average distance from the Earth to the Sun). It takes 687 days to complete one orbit around the Sun; so its year is approximately twice as long as the Earth’s. It rotates once on its axis every 24.6 hours, so it actually has a very similar day length to Earth. It’s also tilted on its axis by 25.2°, again, similar to the Earth’s 23.4°.

Mars is a terrestrial planet, which means that it has the traits of terrestrial planets and is similar to Earth. However, the planet is significantly smaller. Mars has only 15% of Earth’s volume and 11% of our planet’s mass. Its diameter is about half the diameter of the Earth. Mars’ seasons are the most similar to Earth’s seasons due to the similarity in the tilt of the axes. The temperatures on the planet vary from about -140°C during the winter to approximately 20°C during the summers. It takes the planet 687 Earth days to orbit the Sun, and just over 24 and a half Earth hours to rotate the Sun. Mars is about 230 million kilometers from the Sun.

Planet Mars has a very thin atmosphere of carbon dioxide, approximately 1% as thick as the Earth’s atmospheric pressure at sea level. Because of this thin atmosphere, and its longer distance from the Sun, Mars is much colder than Earth. The planet’s average temperature is -46 °C, which means it’s even colder at the poles and during the winter. At the equator, in the summer, temperatures can rise as high as 20 °C.

It’s about half the size of Earth, with a diameter of only 6,792 km. It has an even smaller mass, with just 10% the mass of the Earth. With this smaller size and mass, the force of gravity on the surface of Mars is only 37.6% the gravity you experience on Earth. Imagine weighing 1/3rd less, and being able to jump 3 times as high.

The surface of Mars is dry and dusty, with many similar to Earth. It has mountain ranges and sandy plains, and even some of the largest sand dunes in the Solar System. It also has the largest mountain in the Solar System, the shield volcano Olympus Mons, and the longest, deepest chasm in the Solar System: Valles Marineris. It also seems to have evidence of ancient oceans and streams. But any water that was ever on the surface of Mars dried up billions of years ago. Scientists think that the inside of Mars is similar to Earth, with a dense core (thought to be solid), a rocky mantle and a thin crust. The surface of Mars has also been pounded by impact craters, many which date back billions of years. These craters are so well preserved because of the slow rate of erosion that happens on Mars.

The planet has two small moons, Phobos and Deimos. The moons were discovered in 1877 by the astronomer Asaph Hall and were named after mythological characters. Phobos and Deimos are the sons of Ares, the god of war, in Greek mythology. The Greeks had named the planet Ares after their own god of war before the Romans. Phobos represents fear while Deimos stands for terror or dread. Scientists believe they were asteroids captured by the planet’s gravity. Phobos orbits the planet in just 7 hours, while Deimos takes 1.3 days to go around Mars.

People have been fascinated with Mars for centuries. When telescopes were developed, astronomers were able to see what appeared to be canals on the surface. These sparked speculation that the planet was inhabited and the search for Martians began. Eventually, scientists were able to discover that the canals were really nothing more than extraordinary canyons that crisscrossed the planet. One of the most famous canyons is Valles Marineris, which is 4,000 km long and up to 7 km deep. In comparison, the Grand Canyon is only 446 km long and almost 2 km deep. In addition to these canyons, Mars also had many incredible geographic features, such as Olympus Mon, which is the tallest mountain in the Solar System. Olympus Mon is a shield volcano that at 27 km tall is three times the height of Mount Everest.

Hellas Planita, also called the Hellas impact basin, is the largest crater on Mars. Its circumference is approximately 2,300 kilometers, and it is nine kilometers deep. Many scientists believe that there used to be liquid water in these gullies and channels, which seem to have been caused at least partially by water erosion.  Some of these channels are quite large reaching 2,000 kilometers in length and 100 kilometers in width. Relatively recently, a probe did discover ice water under the surface at both poles. Some astronomers think they planet once had water, but that Mars was unable to retain it due to its weak atmosphere and gravity.

The planet also experiences dust storms, which can turn into what resembles small tornadoes. Larger dust storms occur when the dust is blown into the atmosphere and heats up from the Sun. The warmer dust filled air rises and the winds get stronger.  These dust storms can reach up to thousands of kilometers wide and last for months at a time. When they get this large, they can actually block most of the surface from view.

Mars is the most studied planet in the Solar System after Earth. At the time that this article was written, there were 3 landers and rovers on the surface of Mars, and 3 functional spacecraft in orbit. And more spacecraft will be on their way soon. These spacecraft have sent back incredibly detailed images of the surface of Mars, and helped discover that there was once liquid water in Mars’ ancient history.

One thing that scientists searched for when trying to determine whether Mars could support life is the presence of liquid water. They eventually determined that Mars atmosphere was too thin to allow liquid water to stay in the surface. However, water ice exists on the planet in plenty. The two polar ice caps, Planum Boreum and Planum Australe, are water ice and ice deposits are located around the planet. Mars also has some huge craters, such as the Hellas impact basin.


Fraser Cain is the publisher of Universe Today. He's also the co-host of Astronomy Cast with Dr. Pamela Gay.

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